1. Field of the Invention
This invention relates to a delivery interrupt mechanism for use in a printing machine.
2. Description of the Related Art
It is frequently desirable to be able to inspect the printed output of a printing machine as printing is being carried out. In a typical printing machine, individual sheets of paper sequentially pass through a printing section of the printing machine where they undergo printing and are then forwarded to an output section of the printing machine where the printed sheets are sequentially placed atop one another in a vertical output stack. If the printing machine is operating at a high speed, such as at the rate of several impressions per second, there is insufficient time for the operator of the printing machine to manually remove a printed sheet off the top of the output stack to inspect the sheet before subsequent sheets have settled atop the sheet which the operator is trying to remove. This can result in the sheets at the top of the output stack becoming misaligned and disturbing the neatness of the output stack. Therefore, some printing machines are equipped with a device, commonly referred to as a delivery interrupt mechanism, to temporarily prevent printed sheets from settling on the output stack and thereby give the operator of the printing machine time to remove a sheet from the top of the output stack.
A delivery interrupt mechanism generally includes a rigid finger movable between a retracted and an extended position. In the extended position, the finger projects into a path of movement of the printed sheets and supports the leading edge of the printed sheets to prevent their settling onto the output stack. When the finger is extended, the operator of the printing machine can easily remove a printed sheet from the top of the output stack by hand and inspect the sheet. After the sheet being inspected has been removed from the output stack, the finger of the delivery interrupt mechanism is moved to its retracted position where it is clear of the path of movement of the printed sheets, and the printed sheets which were temporarily supported by the finger are allowed to settle onto the output stack.
However, existing delivery interrupt mechanisms tend to be large and have limited actuating options, so they are difficult to apply to small printing machines having limited interior space.